Pöll Johan J, Hoogeman Mischa S, Prévost Jean-Briac, Nuyttens Joost J, Levendag Peter C, Heijmen Ben J
Department of Radiation Oncology, Erasmus MC-Daniel den Hoed Cancer Center, Rotterdam, The Netherlands.
Med Phys. 2008 Jun;35(6):2294-9. doi: 10.1118/1.2919090.
Advances in image guidance and dose delivery techniques, and increased use of hypofractionation, have led to prolonged radiotherapy fraction duration. This is also the case with robotic radiosurgery, as extensive on-line image guidance procedures, many beams, and usually high fraction doses are used for tumor irradiation. At this institution, early stage non-small-cell lung cancer patients are treated with image guided tumor tracking for respiratory motion compensation. Approximately 130 circular beams and up to approximately 39 000 monitor units (MUs) are used for delivery of a total treatment dose of 60 Gy. The large number of MUs leads to long treatment times and the radiation leakage increases with the number of MUs. Generally, per patient, a single (small) cone is used. To substantially reduce the number of MUs, the authors have developed a new planning strategy for combined use of a small and a large cone. The large cone aims at dose delivery around the PTV center, while the small cone shapes the dose around the (irregular) PTV edges. The authors systematically investigated relationships between the number of MUs, the plan quality, the selected cone diameters, and the beam-direction setup. Plan quality was assessed with the conformity index, mean lung dose (MLD), V20 of the lungs, and by visual inspection. The reduction in MUs was determined by comparing two-cone plans with corresponding one-cone plans that yielded equal MLD, i.e., equal predicted lung toxicity. With the proposed two-cone approach, the required number of MUs reduced by on average 31% (range 4%-56%). The beam-on time per treatment fraction reduced by on average 8 min (range 1-15.2 min). All plans obeyed the clinically applied constraints and were considered clinically acceptable by an involved physician.
图像引导和剂量递送技术的进步以及大分割放疗的更多应用，导致放射治疗分次时间延长。机器人放射外科手术也是如此，因为在肿瘤照射中使用了广泛的在线图像引导程序、多个射束，并且通常使用高分次剂量。在本机构，早期非小细胞肺癌患者采用图像引导肿瘤跟踪来补偿呼吸运动。大约130个圆形射束和多达约39000个监测单位（MU）用于递送60 Gy的总治疗剂量。大量的MU导致治疗时间延长，并且辐射泄漏随着MU数量的增加而增加。一般来说，每位患者使用单个（小）准直器。为了大幅减少MU的数量，作者开发了一种新的计划策略，用于联合使用小准直器和大准直器。大准直器旨在在计划靶体积（PTV）中心周围递送剂量，而小准直器则在（不规则的）PTV边缘塑造剂量。作者系统地研究了MU数量、计划质量、所选准直器直径和射束方向设置之间的关系。计划质量通过适形指数、平均肺剂量（MLD）、肺的V20以及目视检查来评估。通过将双准直器计划与产生相等MLD（即相等预测肺毒性）的相应单准直器计划进行比较，确定MU的减少情况。采用所提出的双准直器方法，所需的MU数量平均减少了31%（范围为4% - 56%）。每个治疗分次的照射时间平均减少了8分钟（范围为1 - 15.2分钟）。所有计划均符合临床应用的限制条件，并被相关医生认为在临床上是可接受的。
